This invention relates to a digitally controlled phase shifter and, more particularly, to a remote controlled subcarrier phase shifter for adjusting the phase of the color subcarrier signal at a color television camera.
In a multi-camera system, each camera must have its subcarrier signal properly phased so that, after all cable delays to a common video switcher, the color subcarrier signals from all of the cameras will be in the same phase at the switcher inputs. In a conventional subcarrier phase shifter system, a rotary switch on the camera enables the operator to select the coarse phase which was the closest to the desired phase. This rotary switch selects sections of a tapped delay line. In the prior art phase shifter system, the fine phase adjustment is provided by a mechanical potentiometer located on the camera that is coupled to a resistance of a resistance-capacitance circuit. The common video switcher is for example located at the operator's control console or at some remote location where there is a monitor to view the phase at the video switcher output. The conventional system requires an operator at the monitor and video switcher and a helper or operator located at the camera for making the adjustments. The system would also require some form of communication between the person located at the camera and the person at the monitor for communicating the information relating to position of the potentiometers and rotary switch and the reading of the subcarrier phase. It is therefore desirable to remotely control the subcarrier phase in the camera. It is also desirable to remotely control these phase shifters by digital signals to more accurately control the phase shift even in a noisy environment.